Main hypothesis: A trial including both dextroamphetamine(Dex) and methylphenidate(Met) will provide better results than a trial including only Met. a)Met and Dex are efficient as treatment for ADHD compared to placebo, albeit Dex has moderately better effect compared to Met. b)At an individual level some of the participants will show positive response to one type of stimulants and no response, mixed response or adverse response to the other type of stimulant. c)Neuropsychological tests and behavioral questionnaires are moderately in agreement but also add unique information in the assessment of the effect of stimulants. d)Qb-test is sensitive and valid as a measure of the effect of stimulants.